.\" Copyright (c) 2001 Mike Barcroft <mike@FreeBSD.org>
.\" Copyright (c) 1990, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
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.\" This code is derived from software contributed to Berkeley by
.\" Chris Torek and the American National Standards Committee X3,
.\" on Information Processing Systems.
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.\"    may be used to endorse or promote products derived from this software
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.\"     @(#)strstr.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD$
.\"
.Dd October 11, 2001
.Dt STRSTR 3
.Os
.Sh NAME
.Nm strstr , strcasestr , strnstr
.Nd locate a substring in a string
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In string.h
.Ft char *
.Fn strstr "const char *haystack" "const char *needle"
.Ft char *
.Fn strcasestr "const char *haystack" "const char *needle"
.Ft char *
.Fn strnstr "const char *haystack" "const char *needle" "size_t len"
.In string.h
.In xlocale.h
.Ft char *
.Fn strcasestr_l "const char *haystack" "const char *needle" "locale_t loc"
.Sh DESCRIPTION
The
.Fn strstr
function
locates the first occurrence of the null-terminated string
.Fa needle
in the null-terminated string
.Fa haystack .
.Pp
The
.Fn strcasestr
function is similar to
.Fn strstr ,
but ignores the case of both strings.
.Pp
The
.Fn strnstr
function
locates the first occurrence of the null-terminated string
.Fa needle
in the string
.Fa haystack ,
where not more than
.Fa len
characters are searched.
Characters that appear after a
.Ql \e0
character are not searched.
Since the
.Fn strnstr
function is a
.Fx
specific API, it should only be used when portability is not a concern.
.Pp
While the
.Fn strcasestr
function uses the current locale, the
.Fn strcasestr_l
function may be passed a locale directly. See
.Xr xlocale 3
for more information.
.Sh RETURN VALUES
If
.Fa needle
is an empty string,
.Fa haystack
is returned;
if
.Fa needle
occurs nowhere in
.Fa haystack ,
.Dv NULL
is returned;
otherwise a pointer to the first character of the first occurrence of
.Fa needle
is returned.
.Sh EXAMPLES
The following sets the pointer
.Va ptr
to the
.Qq Li Bar Baz
portion of
.Va largestring :
.Bd -literal -offset indent
const char *largestring = "Foo Bar Baz";
const char *smallstring = "Bar";
char *ptr;

ptr = strstr(largestring, smallstring);
.Ed
.Pp
The following sets the pointer
.Va ptr
to
.Dv NULL ,
because only the first 4 characters of
.Va largestring
are searched:
.Bd -literal -offset indent
const char *largestring = "Foo Bar Baz";
const char *smallstring = "Bar";
char *ptr;

ptr = strnstr(largestring, smallstring, 4);
.Ed
.Sh SEE ALSO
.Xr memchr 3 ,
.Xr memmem 3 ,
.Xr strchr 3 ,
.Xr strcspn 3 ,
.Xr strpbrk 3 ,
.Xr strrchr 3 ,
.Xr strsep 3 ,
.Xr strspn 3 ,
.Xr strtok 3 ,
.Xr wcsstr 3 ,
.Xr xlocale 3
.Sh STANDARDS
The
.Fn strstr
function
conforms to
.St -isoC .
